Electrolytic device



Nov. 21, 1939. .1. L. COLLINS 2,180,798

ELECTROLYTIC DEVICE Filed July 20, 1956 INVENTOR. JOSEPH L COILINS ATTORNEYS Patented Nov. 21, 1939 Q r 2,180,798

UNITED STATES PATEN T,OFFICE ELECTROLYTIC DEVICE Joseph L. Collins, North Adams, Mass, assignor I to Sprague Specialties Company, North Adams, Mass, a corporation of Massachusetts Application July 20, 1936, Serial No. 91,614

8 Claims. (Cl. 1488) My present invention relates to electrolytic debeen tried without finding an economic and satvices, and more particularly to electrolytic conisfactory solution. While somewhat greater uni densers both of the so-called "wet and so-called formity is obtained by using a very slow etching "dry types. process, i. e., etching in low concentration solu- 6 To increase the surface area of the filming 'elections and at low temperatures, such slow etching, trode and thus of the capacity of the condenser, as it requires one or more hours, results in a poor it is known to subject the electrode to chemical utilization of the equipment, space, and labor, etching prior to its film formation, and various and is therefore uneconomical. etching processes and schedules are used for this Therefore, in spite of the greater variations ob- 10 purpose, whereby a twoto six-fold increase in tained, quick etching with high concentration capacity is obtained, compared with condensers solutions and higher etching temperatures are having unetched electrodes of the same dimenused, with etching times running usually from sions. one to five minutes. I However, in the manufacture of condensers My invention solves the above difficulties and having such etched electrodes, a serious difliculty provides for a very accurate control of the ex- 15 arises, as the capacities of the individual content of etching of individual foils or electrodes, densers will vary within wide limits in spite of a and results in a variation of usually less than most careful adherence to close manufacturing i10%, and even less, of the capacity of the indispecifications and the use of aluminum of the vidual condensers made in accordance with any same origin, and such capacity variations may be given specification. 20 of the order of 1-25% and more, whereas con- My invention is of general utility for both slow densers using unetched electrodes can be conand quick etching processes, and is of particular veniently manufactured within capacity tolerimportance for quick etching processes where its ances of :5 to :10%. superiority is particularly pronounced.

The above wide-range variations in capacity, My invention is essentially a calorimetrically- 2 resulting with etched electrodes, have several controlled etching process, and is based on the contributing factors. realization that in etching aluminum an exother First, the filming metal used, which is usually mic dissolution of the aluminum takes place aluminum, while of high purity still contains whereby heat is liberated incidental to the reacabout .1 to .3% of impurities, and aluminum tion. As the amount of heat so liberated desheets or foils obtained from different ingots and pends uponthe amount of aluminum removed even from the same ingot, may greatly vary withfrom the surface during the etching, the total in the above limits as to he total amo and amount of heat so liberated is a direct measure as to the substances forming these impurities. of th t tal amount of aluminum removed from On the other-handJhe amount and composith t h d urfa 35 tion of such impurities even in case of such com- I have als found that the total amount of mapa y s al s, greatly affect t rysterial removed from the etched aluminum inditalline structure o e aluminum and its cates with considerable accuracy the extent of 01 during etchingetching of the foil, provided the etching takes 40 secondly, the grain Structure of the aluminum place under such conditions that the:etching so- 40 and its reaction to etching is also dependent lution has a free and uniform access to all surface variations in its heat treatment and working. portions of the aluminum to be etched, and to Thirdly the surface conditmn of the aluml' some extent, that the volume of the etching solu- E g g i g i fi of 'gf. 2 2 tion is sufliciently large as to prevent during the 46 :33? g fi g g g 213: g z fi it is etching any important change in concentration of the etching solution.

general practlce to clean the alummum Surface One object of my invention is therefore to proprior to the etching, these effects are not fully eliminated and affect the etching of thealumi- Vlde an etching process m which by means of ex- 50 num surface.

All of the above factors contribute to cause the etchmg solutlon the extent of the etchmg of the aluminum to etch at difierent rates under iden filming e o s is controlled within ve y actical etching conditions. curate limits.

Various attempts to check and control the A further object of my invention is to provide a s'etching, so as to get more uniform results have quick etching process whereby the extent of etchact checking of the temperature rise of the 50 ing is automatically indicated and controlled by the temperature rise of the etching solution.

A still further object of my invention is to provide an etching process by means of which, not- 5 withstanding the usually occurring variations in the impurities of the filming metal, its grain structure, surface condition, etc., the extent of etching is kept closely uniform so that condens- ,ers having etched electrodes can be conveniently 10 manufactured within capacity tolerances of i 10 and even less.

Other objects of my invention will appear as the description progresses.

- In the drawing forming part of this specifica= 315 tion:

Figure 1 is a schematic diagram of an etching installation in accordance with the invention;

Fig. 2 is a perspective view of corrugated electrodes for wet electrolytic condensers stacked for 20 etching;

Fig. 3 is a top view oi two endless foils rolled together in a compact form for insertion in the etching bath.

Referring to Figure l, the etching tank is a 25 container suitable to hold a sumcient amount of etching solution, for example 30 gallons for 5,000 to 10,000 square inches of aluminum surface to be simultaneously etched, and is made of a suitable material which is not attacked by the etching solution, for example glass, wood, stoneware,

no solution, are immersed in the etching solution,

for example by being placed on the supports 6- 1. the supports being of a material which is not attacked by the etching solution.

Immersed in the etching bath is a mercury coil-- 45, umn thermometer 5. Two contact wires d and l are air-tightly sealed through the wall of the thermometer and so disposed that the contact is always electrically connected through properly acid-proofly insulated leads with the mercury 54) column 8 of the thermometer, whereas the mercury 8 only contacts with I when the etching bath has assumed a certain temperature, i. e., the one at which the etching is completed. The contacts 6 and l are connected in circuit in series with 55 a battery 9 and a buzzer G0, which circuit is closed to sound a warning when the etching bath assumes the above referred to temperature.

It should be noted that the thermometer and the warning arrangement may be of any other so suitable type; also, while I usually prefer to use such audible or visible warning device, such device can be dispensed with and observation of the thermometer left to the operator.

As stated before, the heat developed in the solution during the etching, and thus the temperature assumed by the etching solution (with certain corrections to be made and later referred to) gives a measure of the total amount of aluminum dissolved from the surface subjected to to etching, and also with a very good degree of accuracy the extent of the etching of the foil.

The end temperature, i. e., the temperature at which the etching is completed, can be determined for any specific case either by mp e 75 tion or expermentally.

The computation of the end temperature of the etching solution is essentially a calorimetric computation, applied to the particular problem involved, and the general steps which I shall give below will sufiice without further details to enable one skilled in the art to make such computations.

I first determine the heat capacity and total heat content of the etching solution at the starting temperature, i. e., at the temperature at which the aluminum to be etched is inserted into the solution.

After this I determine the volume and weight of aluminum to be removed by the etching. For this purpose I determine the total surface area of the aluminum exposed to the solution and the average depth of etching, i. e., the average thickness of the aluminum layer to be removed. I have found that within a fairly wide range of composition of the aluminum, there is a definite relationship between the average depth of etching and the so-called etching ratio. The latter ratio gives the increase of capacity of an etched electrode condenser compared with the capacity of an otherwise identical condenser using an unetched electrode. For L example, to obtain an etching ratio of 5 it is necessary to etch to an average depth of about .007" measured from the surface of the aluminum.

After having determined the amount of alumimum to be removed, I compute the total amount of reaction heat liberated incidental to such re moval. While the heat of reaction taking place in such removal of the aluminum somewhat varies with the etching solution used and the etching temperature, it is in average roughly about 150,000 calories per gram atom of aluminum.

The above total reaction heat raises the temperature of the etching bathand the temperature is computed in known manner from the original heat content of the solution, the heat developed in the reaction and the heat capacity of the installation including the etching solutions, electrodes, supports, etc.

For exact computation certain corrections have to be made because of the heat losses due to conduction and radiation, and the variations in the specific heat of the etching solution with the temperature, etc.

As stated, instead of computing the desired final etching temperature I can determine it experimentally.

For the sake of greater uniformity, I prefer as a rule to start the etching operation always at a definite initial temperature of the etching solution, and for this reason I prefer to use a metal tank so that between the etching of consecutive batches of electrodes, the solution may be quickly cooled down to the same starting temperature, which I select as a rule somewhat above the prevailing room temperature.

While the metallic container increases the heat losses, correction can be conveniently made for such, losses, and furthermore, because of the short etching times I usually prefer to use 1 to 5 minutes) the heat losses in themselves are not necessarily important.

Sometimes, to permit a better utilization of the equipment, consecutive batches of electrodes are etched without permitting the solution to cool down to the same initial temperature. In such case, the change in heat of reaction and specific heat have to be compensated for various temperatures, and the predetermined temperature 7 rise or end temperature has to be determined for each particular starting temperature. This can again be done either experimentallyor by computation.

solutions of hydrochloric acid, and use the lower concentrations for higher starting temperatures and/or longer etching times and vice versa.

For example, when starting etching at C. and using an etching time of the order of one to five minutes (usuallyaboutthree minutes) I use chloride.

as a rule acid concentrationsof 12% and 15%; whereas with higher starting temperatures, for example C. and the above etching times, I prefer to use concentrations from 9% to 12%.

It should be noted that even fairly wide variations in concentration will not affect the accuracy of my process except that they may affect the duration thereof. 4

Instead of using hydrochloric acid solutions I may use a weak solution of hydrochloric acid together with salts of metallic ch1orides,'for example of nickel chloride, manganese-chloride. copper chloride, and in some cases also sodium Furthermore, instead of hydrochloric 5 acid other acids may be used, for example,'trichloracetic acid, either aloneor 'together with hydrochloric acid.

It should be noted that the free access of the etching solution to the electrode is of vital importance, as unless the solution has proper access to all surface portions of the aluminum, excessive temperature rises might occur locally in portions of the aluminum, which would result in uneven etching.

Thus the solution, besides having proper access to all portions of the aluminum for its proper etching, should also have free circulation for equal distribution of the heat and concentration. While artificial agitation of the etching solution can be provided for, as a rule this is unnecessary as a natural agitation takes place on account of the evolution of hydrogen gas which accompanies the etching process.

It should be noted that under certain circum-' stances a very high initial rate of etching may take place, which results in the formation of a gray to black deposit on the surface of the aluminum, which has an effect on the character of the etching.

The formation of such a deposit does not form part of this invention, and to obtain the usually desired results when such high rates of reaction are encountered accompanied by such black films, I prefer to interrupt the progress of the etching in the hydrochloric bath by removing the aluminum from this bath and immersing it into an alkaline solution, for example into a solution of sodium hydroxide. the black film on thesurface of the aluminum into a white film, or removes it altogether; after this the aluminum may be reimmersed in the etching solution and the etching reaction allowed to proceed until the predetermined temperature rise is accomplished.

In carrying out this modification of my process,

Such a treatment convertsthe total temperature rise remains the same as if the etching 'had been uninterrupted. Thus in etching a batch of anodes where the predetermined temperature rise in the" etching solution'is from 25 0. to 35 'C., I may interrupt the etching when the temperature reaches 28 C., and after treating the anodes in a caustic solution, replace them in the etching solution at 28 C., and then allow the temperature of the solution to reach 35 C.

When etching batches of corrugated or pleated electrodes, special measures may be necessary to assure proper access of the solution to all portions of the corrugations, and at the same time permit eflicient utilization of the etching equipment. For example, when etching the pleated electrodes a 30 shown in Fig. 2, I stack batches of electrodes sothat the longitudinal axes of successive electrodes are perpendicular to each other.

When etching foils of large lengths, for example so-called endless aluminum foils, and which after their etching are usually submitted to a continuous film-forming process according to the copending applications Ser. No. 548,270, filed July 1, 1931, and Ser. No. 741,493, filed August25, 1934, of Preston Robinson, now respectively United States Patents Nos. 2,057,314 and 2,057,315, issued October 13, 1936, to make it pos- 'sible to etch the foils in a compact form,'I use proper access of the solution would not 'be 1m sured. Y

After the etching has been performed, the corrugated foil 36 prior to film formation is preferably smoothed out by passing it through rolls, although with special forming equipment corrugated foils can also be properly filmed.

' While I have described my invention in connection with specific examples and specific applications, I do not wish to be limited thereto, but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What I claim is:

1. In the manufacture of electrolytic condensers, the process which comprises the steps, immersing aluminum electrodes in an etching bath comprisinga 5% to 20% solution of hydrochloric acid, and removing the etched aluminum electrodes from the bath when the bath temperature, due to-the heat developed by the exothermic reaction between said electrodes and said acid, has risen by a predetermined value above its initial value. '2. The process of manufacturing electrolytic condensers having etched electrodes with an etching ratio between 3 to 6, comprising the steps of subjecting the electrodes to etching for a duration of about 1 to 5 minutes, and controlling, by the amount of heat developed by the exothermic reaction of the etching, the extent of etching of the electrodes within a 15% to :10% accuracy.

3. In the manufacture of electrolytic condensers, the process which comprises, immersing filming electrodes in an acidic etching solution, interrupting said etching and placing said elec- "trodes into an alkaline solutionto remove undesirable deposits formed on said electrodes, and subsequently replacing the electrodes in said acidic solution to complete the etching.

4. In the manufacture of electrolytic condensers, the process which comprises, placing filming electrodes in an acidic etching solution having a predetermined initial temperature, interrupting the etching and placing the electrodes inan alkaline solution to remove undesirable deposits formed on said electrodes, and subsequently replacing the electrodes in said etching solution at the same solution temperature at which the etching has been interrupted, and maintaining said electrodes in said etching solution until the solution, in View of heat developed by the exothermic reaction between said electrodes and said solution, has assumed a predetermined temperature rise from its initial temperature.

5. In the manufacture of electrolytic condensers, the process which comprises, subjecting in an etching solution filming electrodes to chemical etching, measuring the temperature rise caused by the exothermic reaction, and utilizing said temperature rise as an indicator or the degree of etching.

6. In the manufacture of electrolytic condensers, the process of etching filming'electrodes comprising determining the amount of a given electrode -metal consumed by a given etc-hing solution in terms of the temperature rise of said solution caused by the exothermic reaction between said electrode metal and said solution during the dissolution of a given amount of the electrode metal, immersing an electrode of the said metal in said etching solution, raising the temperature of the etching solution by exothermic reaction between said electrode and said etching solu on, and interrupting the etching when said etching solution has reached the predetermined temperature corresponding to the amount of electrode metal to be consumed in the etching process.

'7. In the manufacture of electrolytic dondensers, the process of etching aluminum electrodes comprising determining the amount of aluminum consumed by a hydrochloric acid solution of a given concentration in terms of the temperature rise of said solution caused by the exothermic reaction between said aluminum and said solution during ,the dissolution of a given amount of the aluminum, immersing an"aluminum electrode in said solution, raising the temperature of said solution by exothermic reaction between the aluminum electrode and said solution, measuring the temperature rise of the solution due to said exothermic reaction, and interrupting the etching at the point in the temperature rise of the solution which indicates the dissolution of the amount of aluminum of the electrode sought to be dissolved in the etching process.

the etching at a point in the temperature rise JOSEPH L. COLLINS. 

